The present invention relates to a valve timing adjuster for changing phase difference between a cam shaft and an output shaft during operation of an engine.
A valve timing adjuster disclosed in Japanese Patent Unexamined Publication No. 61-268810 has a ring gear whose radially inner periphery and radially outer periphery include respective sets of teeth at least one set of which is composed of helical teeth, a pulley which engages with the teeth of outer periphery of the ring gear and which is driven by an engine and a cam shaft which engages with the teeth of inner periphery of the ring gear, wherein the ring gear is moved axially by a hydraulically-operated actuator so that the pulley rotates on the cam shaft. In the conventional valve timing adjuster, the helical teeth slide on the teeth engaging therewith in the longitudinal direction of teeth for rotating the pulley on the cam shaft. Therefore, a great frictional force is generated between the teeth engaging with each other.
Since the hydraulically-operated actuator has an oil chamber, a small time lag is needed in order that the pressure of oil chamber reaches a predetermined degree. Therefore, the response speed of conventional valve timing adjuster is low.
Furthermore, since the conventional valve timing adjuster includes many friction regions, for example, between the herical teeth engaging with each other and in the hydraulically-operated actuator, the durability of valve timing adjuster is low.
Furthermore, since pipe lines are mounted on the engine to feed hydraulic oil from a hydraulic source to the hydraulically-operated actuator, the engine must be modified and the cost of product becomes high.